Спиральный квадрат

program SpiralSquare;

uses Graph, Crt;

const
	min = 1;
	l0  = 300;
	da  = pi/20;
	x0  = 320;
	y0  = 240;
var
	gd, gm: Integer;
	x, y  : Integer;
	l     : Real;
	a     : Real;
	
procedure Rectangle_(d, u: Real);

var
	x1, y1: Integer;
	x2, y2: Integer;
	x3, y3: Integer;
	x4, y4: Integer;
	
begin
	x1 := Round(x0 + d * cos(u +   pi/4));
	y1 := Round(y0 + d * sin(u +   pi/4));
	x2 := Round(x0 + d * cos(u + 3*pi/4));
	y2 := Round(y0 + d * sin(u + 3*pi/4));
	x3 := Round(x0 + d * cos(u + 5*pi/4));
	y3 := Round(y0 + d * sin(u + 5*pi/4));
	x4 := Round(x0 + d * cos(u + 7*pi/4));
	y4 := Round(y0 + d * sin(u + 7*pi/4));
	Line(x1, y1, x2, y2);
	Line(x2, y2, x3, y3);
	Line(x3, y3, x4, y4);
	Line(x4, y4, x1, y1);
end;

begin
	gd := Detect;
	InitGraph(gd, gm, 'c:\bp\bgi');
	SetColor(14);
	l := l0;
	a := 0;
	repeat
		Rectangle_(l, a);
		a := a + da;
		l := l * sin(pi/4) / sin(3*pi/4 - da);
	until (l <= min) or (KeyPressed);
	Readkey;
	CloseGraph;
end.